1. The Field of the Invention
The present application relates to the field of protective coatings and laminates. More particularly, the present invention relates to a method of applying a durable optically transparent laminate to a windshield for protecting the windshield from damage due to gravel, rocks or other debris impacting the windshield, as well as protected windshields made thereby.
2. The Relevant Technology
Every year, millions of windshields are damaged by rocks or other debris that impact the windshield. Winter is particularly hazardous in many areas where environmental constraints on the use of salt to control icy surfaces result in a great deal of sand or other biodegradable substances being used. This sand, coupled with rocky areas as well as natural rubble and construction debris, has created a year-round hazardous situation for glass (and/or laminated) windshields in any overland vehicle or glass in other equipment, as the sand and other rubble are thrown up and collided with windshields.
If the damage is small, such as a small chip in the windshield, it can often be repaired in situ. Large damage such as larger chips and cracks, however, requires the windshield to be replaced. The cost of repairing or replacing each windshield ranges up to hundreds of dollars or more. Accordingly, there is a continuing need for methods to reduce windshield replacements by reducing windshield damage from impacting debris.
Previous attempts to provide exterior films to protect windshields from damage have failed or are limited for any of a number of reasons. Such reasons include, for example, that the films: do not cover the entire glass; do not adhere to the glass; do not conform to a curved windshield; are not UV stable over the long term; the materials readily scratch from windshield wipers and car wash brushes; and/or have poor optical quality due to inferior film or adhesive restrictions.
For example, U.S. Pat. No. 6,634,695 (“the '965 patent”) discloses an impact resistant barrier around the periphery of a windshield. Generally disclosed barrier materials in the '965 patent include clear polymeric films as well as opaque materials such as rubber, plastic, or metal. Particularly, one suitable barrier material disclosed by the '965 patent is Scotchcal™, an 8 mils urethane film sold by 3M. By limiting the extent of these clear and opaque barriers to the periphery, high visibility is maintained in the center of the windshield while protection is provided around the periphery. This approach is clearly limited in that the barriers are not suitable to cover the entire windshield. Thus, in order to maintain a suitable visibility where the barrier materials are applied, the '965 patent limits itself to protecting only those portions of the windshield where high visibility is not necessary.
Attempts thus far at providing a clear protective film to cover an entire automobile windshield have failed for various reasons, typically because the suggested films are not sufficiently transparent, distort the view, are not UV stable, or scratch easily. For example, the transparent laminate materials currently commercially available as Scotchgard Anti-Graffiti Window Film AG-4 and Scotchgard Anti-Graffiti Window Film AG-7 from 3M Corporation were tested for windshield applications. These films were found to be unsuitable because they do not provide sufficient scratch resistance for windshield applications and the underlying PET is not UV stable. Under the demanding conditions a windshield places upon a laminate film, the AG-4 and AG-7 were both been found to degrade and scratch more than is acceptable.
Accordingly, there is a continuing need for new and improved methods and devices to protect entire windshields from damage without significantly reducing the optical qualities of the windshield.